Following Armadillo's lead, I figured it would be a good idea to have a SpaceFellowship forum with a Q&A thread in addition to our company blog , and my personal blog, Selenian Boondocks. If you have any questions about Masten Space Systems, our vehicles, engines, markets, Lunar Lander Challenge plans, or anything else for that matter, just post them here. I'll try to include links and brief summaries to our progress updates, and maybe some eyecandy from time to time.

Awesome! I have been keeping up with your work from time to time and I like what I see. I'll be interested to keep following it. I have one question (which shows that I really haven't done my homework, but oh well): how many engines does the XA-1.0 have? I see that you are developing some sort of swingable engine mount, which suggests a single gimbaled engine like Armadillo, but I have also seen references to "engines" (plural) on the vehicle.

_________________"The rockets are burning, the dreamers are at full swing/ And you know in your heart that the farsighted see better things." ~ "Farsighted" by Five Iron Frenzy

Awesome! I have been keeping up with your work from time to time and I like what I see. I'll be interested to keep following it. I have one question (which shows that I really haven't done my homework, but oh well): how many engines does the XA-1.0 have? I see that you are developing some sort of swingable engine mount, which suggests a single gimbaled engine like Armadillo, but I have also seen references to "engines" (plural) on the vehicle.

Before I answer your other questions, why don't a clarify a little bit about our vehicle designations. At MSS the first commercial vehicle we're working on developing is called XA-1.0. XA-1.0 will be able to deliver at least 100kg to a 100km suborbital altitude. The XA-0.x series of incremental test vehicles will lead up to this first commercial vehicle. The first in that series, XA-0.1 is the one we were showing off last week at the X-Prize Cup, and the one we plan on getting flying in the near future.

I can't go into too much detail (especially since some of it is subject to change as time goes on), but here's a brief overview of the first three XA-0.x vehicles (at least as far as they have been solidified):

XA-0.1:
-pressure fed, LOX/Isopropanol design
-about 320lb of propellant, 1000lb drymass
-uses 4 of our 500lbf XVT-500LIT-4 engines
-each engine is throttleable over at least a 3:1 range
-four fixed landing gear similar in design to the ones used on the Japanese RVT vehicle
-Ethernet based communication between avionics and engine computers
-each engine has single axis hinging and differential throttling for thrust vector control
-Frontier Astronautics designed avionics
-Maximum flight time: 60s

Anyhow, that's a brief summary for now. Details can and probably will change as time goes on. But that's what we're working on. We're going to try and field at least a Level One capable vehicle this next year, and if time and funding permits, we'll field the Level Two capable vehicle as well. Fortunately, the prize levels happen to line up fairly well with the vehicles we were planning on making anyway, even if the prize hadn't been offered.

Awesome, thanks for the outline! I messed up when I asked about the XA-1.0, I had the 0.1 in mind. You answered my question though: single-axis hinge for the motors, four of them, and differential throttling. That's an interesting configuration. I imagine that makes for some complex software.

Good to see you planning for the next X-Prize cup!

_________________"The rockets are burning, the dreamers are at full swing/ And you know in your heart that the farsighted see better things." ~ "Farsighted" by Five Iron Frenzy

Awesome, thanks for the outline! I messed up when I asked about the XA-1.0, I had the 0.1 in mind. You answered my question though: single-axis hinge for the motors, four of them, and differential throttling. That's an interesting configuration. I imagine that makes for some complex software.

The math behind the software is a bit complex, for instance, you need more detailed info on stuff like the inertia matrix for the vehicle and the response times for the throttling and hinging. But from what I can tell the actual software implementation isn't really that difficult for someone experienced with State-Space Control theory. Now, trying to do that using classical control theory would be rather interesting. Fortunately, I'm not involved in the coding one way or the other--I just design, build, and test rocket engines.

Solo wrote:

Good to see you planning for the next X-Prize cup!

Anyone who actually wants to compete next year better be well into their planning by now or they don't stand a chance. Since there are now only two places for each prize level, that means that any potential competitor has to assume that they'll only get prize money if they not only meet the bare requirements, but if they can win on the flyoff. Which takes a lot of time, money, and flight experience.

Got a question for you: will the 0.x series only be used for basic flight tests -- hover, translate, land, and so forth -- or will they be capable of reaching any interesting altitudes? I imagine they won't have huge payloads, but it does sound like the later vehicles must have enough delta-v to get in the vicinity of 100km, if not beyond. Could be a revenue source; also, I confess a great fondness for John Carmack's vertical drag racing notion, and it'd be nice to see another company with the ability to compete. I suppose a related question would be whether you plan on doing aerial restarts with any of these vehicles...

What's the engine like? I understand it uses regenerative cooling. What's the max continuous firing duration? What about total? Does it wear significantly? What's the thrust and ISP? What are the materials? What kind of injector? What are the issues now? How many iterations have you gone through? Any dead ends?

I understand you can't probably answer many of these in much detail, but something...

Got a question for you: will the 0.x series only be used for basic flight tests -- hover, translate, land, and so forth -- or will they be capable of reaching any interesting altitudes?

Well, XA-0.1 is definitely a low altitude hover, translate, land vehicle. XA-0.2 will likely have a bit of an aeroshell, so we *might* do some boosted hops on it after the X-Prize Cup. XA-0.3 will have a good aeroshell on it, but large fixed landing gear. We'll probably be able to take it relatively high, just not too fast until we've designed retractable versions of those landing gear (XA-0.35 maybe?). Once we have that, we're planning on slowly expanding the envelope, adding RCS engines, improving the aeroshell, and working our way up to 100km.

As it is, our first generation regen engines completely blew away the original conservative target numbers for XA-1.0, and it's looking like the Delta-V numbers for 100km that we were originally using were also rather pessimistic. What this means is that "XA-1.0" will likely come shortly after XA-0.4 or 0.5, with the higher performance XA-1.5 coming after XA-0.8 or 0.9.

But yeah, basically we intend to expedite the delivery of our first vehicle capable of revenue service.

skybum wrote:

I imagine they won't have huge payloads, but it does sound like the later vehicles must have enough delta-v to get in the vicinity of 100km, if not beyond. Could be a revenue source;

Exactly.

skybum wrote:

also, I confess a great fondness for John Carmack's vertical drag racing notion, and it'd be nice to see another company with the ability to compete.

We like the idea too. Our Level 2 vehicle would make a fairly decent vertical dragster, if we can get it put together and debugged in time for X-Prize Cup, and if we can get FAA approvals, maybe we'll see if we can arrange a VDR flight going head-to-head against John. But our main focus at the moment is our critical path toward XA-1.0. We have a clock ticking on that one (we promised something like June or July 2008 for first flight of a payload to 100km or people can start asking for refunds), so it's our main priority.

skybum wrote:

I suppose a related question would be whether you plan on doing aerial restarts with any of these vehicles...

You pretty much have to for suborbital flights, especially if you want to do anything scientifically interesting (microgravity, earth/space observation, etc) when you get there. Part of the reason why XA-1.0 has 8 engines, with two independent feed systems (one for each 4 engines), and dual igniters per engine is to insure that when we push that *light engines now* button, that we get sufficient numbers lit to avoid going splat.

We do still have some work before we'll say that our engines are qualified for in-air relights, but that's been a goal from the start.

What's the engine like? I understand it uses regenerative cooling. What's the max continuous firing duration? What about total? Does it wear significantly? What's the thrust and ISP? What are the materials? What kind of injector?

Ok, taking your questions a bit out of order,

Our engine is a 500lbf, throttleable regen cooled engine. Chamber is made of a copper alloy, outer jacket is made of an aluminum alloy, and when we go back to a Chamber-Saddle-Jacket design, we'll go with a saddle made of an aluminum alloy. The injector is a pintle-style injector, like what SpaceX uses. Our injector is a fixed geometry injector, which means it's actually rather simple mechanically, in spite of the good throttleability.

The max thrust we've run the thing up to is about 500-520lbf, but theoretically, with our throttle valves and tank feed pressures, we could probably take it up to about 600lbf.

Our longest firing to-date was last week in Las Cruces--94.3 seconds at full throttle. For a regen engine, once it reaches thermal equillibrium (which happens after like 10-15 seconds or so), you can theoretically keep it going so long as you can keep shoving propellants into it. With a slightly different mixture ratio, we could probably get 100-120 seconds at full throttle with our current stand, or up to 200+ seconds at 50% throttle.

The tanks on our XA-0.3 have enough capacity to fire a single engine at full throttle for something like 20-30 minutes. So maybe we'll do a run or two like that to see how it fairs over that long of a time. Maybe there is some sort of weird second order effect lurking in there. I don't know. I know that the Russians supposedly hooked one of their engines up to a tanker car load of propellants and ran it for some ridiculously long amount of time, but I'm not sure which engine, or how long.

As for erosion, no noticeable signs yet.

meiza wrote:

What are the issues now? How many iterations have you gone through? Any dead ends?

Well, the engines themselves are just about ready to be qualification tested for our first flight vehicle. We're still sorting out some less than sufficiently robust instrumentation issues, but other than that this first rev of engines is pretty much ready to go. After these are in service, we'll get going on a next rev that lightens things up, packages them better, and goes to a more convenient gimbal mount and possibly sensor scheme.

We've gone through several iterations now:
XVT-500LIT-1 was a water cooled "piston nozzle" design with heat flux sensors to help us dial in our performance numbers, ideal L*, and figure out the thermal environment so we could move on to designing the regen cooling system. A flawed joint/seal design issue combined with a controls issue killed the thing on its second firing.

XVT-500LIT-2 was a fuel/water cooled (but not full "regen") piston nozzle design. We got the joint design issues resolved, and had over 120 firings on the design. Iterated a bunch on the injector design, and took a lot of thermal data. Cumulative firing time on that one was probably about 6 minutes.

XVT-500LIT-3.5 was the spiral regen design that was our first attempt at a regen engine. It wasn't supposed to be steady-statable, it was just supposed to provide us enough information to get the design right for the next rev, but it worked. Unfortunately, since the guys making it took so long, it ended up not arriving till after our next engine (the XVT-500LIT-3.75), so we only actually started firing it about two weeks ago. We were doing throttle testing, and didn't want to risk a good engine on it, so we tossed this one in. That was the one we used in Las Cruces. It's total firing duration is something like 250 seconds or so (all of it in the past two weeks).

XVT-500LIT-3.75 was an axial regen version of the -3.5 design. Same flow area, but axial channels. We did this one because the machinist was having issues with cutting the spiral groove for the -3.5 design, and ended up taking two months longer than he promised. This was the one we first steady stated back in March or April. It's had over 100 firings on it, with a maximum duration of about 45 seconds. Total burn time over 450 seconds.

XV-500LIT-4 this is the current flight engines. They are very similar to the -3.75 engines, except for having a slightly different cooling inlet design (to work with the flight outer jackets), as well as having a slightly different head-end configuration. We'll be qualifying these this week.

XV-500LIT-5 this is the Chamber Saddle Jacket design. We were going to fly with these, but caught a small manufacturing error due to a CAD drawing error I made. We're going to work on fixing those and testing them in the near future. They weigh something like half as much as the -4 designs we'll be flying XA-0.1 on.

Oh, a quick nomenclature description. X stands for eXperimental, V for Vernier, the first T for Teststand (ie non-flight), the number is the thrust in pounds (we'll probably start using K's in there once we go to bigger engines), L is for Liquid Oxygen, I is for Isopropyl, and T is for throttleable. Then the number after the dash is the rev number.

Anyhow, that's probably more detail than you wanted, but there you go. Seeing as how none of us had fired a liquid fueled biprop engine a year ago, we've come a very long way. Our engines are robust, efficient, and reliable, and they're getting better all the time.

So all that X Prize P.R. about civilians in their garages designing the Next Lunar Lander was just a cover story for the real work going on out there, hm?

The X prize does seem to like to build this all up as exactly what you describe. However, this is not the case. The groups that are actively and realistically participating in this are much more than a few enthusiasts in a garage.

These are viable engineering companies with access to resources that amateur groups do not have. While our resources are small compared to companies like Lockeed or Boeing, we still have access to the facilities, tools, and knowledge base we need to be able to get this sort of work done.

Any group of individuals that intends on joining the party had better be very well funded and organized beyond the level of any enthusiast group I have seen.

Yeah, I just got my hands on the recent issues of Pop. Mech. and Pop. Sci. with their pre-XPC articles on both MSS and Armadillo. You are right, they wanted to play up the 'human interest' aspect of things, as my composition teacher termed it.

_________________"The rockets are burning, the dreamers are at full swing/ And you know in your heart that the farsighted see better things." ~ "Farsighted" by Five Iron Frenzy

Just wanted to post a quite update to let people know what we've been up to lately. I'll probably write up a more formal entry on the MSS blog before the end of the week, but people have been asking me so I figured I'd give a quick core-dump.

So, before the X-Prize Cup, we were trying to get our last development project (the valve dynamic throttling control) working correctly. We had done several firings the night before we headed out to the X-Prize Cup using the setup, and had found a really weird low-frequency instabillity that we had never seen before with our engines. We couldn't solve it that night (in spite of staying at it until 3am the next morning), so we went back to PLC mode for our firings in Las Cruces.

After we got back from Las Cruces, we went back to the water flow stand, and I suggested we do a quick flow test with a visual flow meter to verify that our flight valves had the same flow characteristics (with respect to angular position) as the two prototypes that we had been using previously. Our supplier for the valves was super-competent, and the prototype valve calibration had matched up so well with our verification test previously, but I was in a paranoid mood.

And it payed off. When we started at the lower throttles, we found a flow oscillation, that I recognized as being about the same frequency as the oscillations we had seen in the test firings before Las Cruces. So, we spent the next two or three days going over the entire controller and servocontroller setup with a fine toothed comb, and eliminated the problem. It ended up being a combination of three really subtle things (one a bug in the new firmware they sent us, one a hardware noise issue, and one a subtle grounding issue), but in the end we completely stomped that out.

We then went out today to verify the thing worked, tried several firings, and the combustion was a lot more stable than those runs the night before we packed up. Unfortunately, we've been having issues with getting half-full LOX dewars here in Mojave, and we ran out of LOX before we could do enough throttle testing points to verify that our dynamic throttling works correctly. So we'll have to wait until the next Praxair shipment arrives on Wednesday, but with that valve-twitch gremlin squashed, I have a lot more hope that things will just work. Once that's done, and once we've done a test series to verify the reaction time of the throttling system, that development task will finally be closed.

Then we get to put together 3 more engine computer boxes, 3 more servocontroller boxes, a bunch of harnessing, the four flightweight engines (and accompanying igniters), qualify everything, and then we're on to vehicle testing!